Mixers for heat treatment and/or for cooling a mixture of solid particles in a mixing vessel that has at least one heat-treatment central channel that at least partially gets in contact with the solid particles to be heat-treated are known. These mixers are typically used to cool a mixture of particles which has previously been mixed in a mixer. Therefore, such mixers are also designated as cooling mixers. Typically a so-called heating mixer is placed into the flow ahead of such a cooling mixer in the procedural chain. The product to be mixed is poured into it. In the course of the mixing process the particle mixture is heated by friction, so it then must be cooled to give the mixture further treatment. To do this the mixture is fed to a cooling mixer, which typically is attached directly to the outlet of a heating mixture. Such cooling mixers are often used with high-performance mixing systems for raw plastic products, such as powdered plastics for PVC manufacture.
Previously known cooling mixers have a vessel with a cooled inner wall. The vessel is designed with a dual wall, with cold water being channeled into or through the channels forming the dual wall. Therefore a part of a cooling channel forms the interior wall of the vessel, with the product for mixing being fed past this cooled wall section during the mixing process. In the vessel there are motor-driven mixing tools for circulating the mixture to be cooled. Thus, the mixing tools with their motor drive represent a circulating device to circulate the mixture to be cooled.
The vessel of such a cooling mixer typically has a circular cross sectional surface. The horizontal cooling mixer and vertical cooling mixture are different depending on a horizontal or a vertical alignment of the vessel. In both cases, the inner side of the annular wall of the vessel forms the cooling surface at which the mixture is cooled during circulation s by the mixing tools. Each mixing vessel has available two attachment connector pieces, one by which the cooling mixer is attached to the output of an upstream high-performance mixer, and another one for expelling the cooled material for mixing. With vertical cooling mixers, the filling connector piece is attached to the top cover flap. The emptying connecting piece is on the radial outer side of the annular sidewall. With a horizontal cooling mixture, the outlet connector piece and the filling connector piece typically are in the middle of the overall cylindrical cooling vessel, with the filling connector piece at or near the upper apex and the outlet connector piece at or near the lower apex of the mixing vessel.
Wear is observed on the vessel walls with known cooling mixers, particularly in the areas of the motion paths of the mixing tools, even if they do not actually touch the inner side of the vessel walls. This is not desirable. In addition, the cooled mixture can be contaminated by the material that is rubbing off. Care must be taken when such a cooling mixer is operated that the procedural time that is necessary to cool a batch of mixture is not longer than the procedural time needed to conduct complete the mixing, for example by an upstream heating mixer. This is especially true with mixing of a temperature-critical mixture. As for example, this is decisive when mixing powdered plastic for PVC manufacture. Inside the cooling mixer within such a procedure, not only must the inserted material for mixing be cooled to the needed temperature, but also the additional treatment must have been concluded, namely filling the vessel and expelling the cooled mixture.
It is desirable for the inserted material to be cooled as uniformly as possible when such a cooling mixer is in operation. Due to the placement of the outlet connector piece on the cooled wall of the vessel, this part of the vessel does not contribute to the cooling of the inserted mixture. Owing to this, in that area in which the material to be cooled is in contact with the inner vessel wall, cooling surface is lost.
It is expensive to clean such a previously known cooling mixture when one switches over from one material for mixing to be cooled to another one. This is due a portion of the mixture cannot be emptied using the normal means due to the geometry of the mixing vessel, and therefore remains in the mixing vessel. Additionally, the mobile tools for circulation must be cleaned.
The foregoing example of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.